(1) Field of the Invention
The present invention relates to an Al.sub.2 O.sub.3 -TiC sintered product adapted to being machined on its surfaces by the irradiation with ions such as of ion milling method or reactive ion etching method (REI method). More specifically, the invention relates to an Al.sub.2 O.sub.3 -TiC sintered product that is used as a substrate for thin-film magnetic heads, and is further used for jigs and measuring instruments.
(2) Description of the Prior Art
Among the magnetic heads, a thin-film magnetic head forms a magnetic head circuit on the surface of a predetermined substrate relying on a thin-film-forming method such as sputtering or the like, and has been vigorously developed since it enables the magnetic gap to be finely controlled as well as a high-density recording to be accomplished. In the substrate used for the thin-film magnetic head, the surface that faces the magnetic recording medium works as an air bearing surface of a slider and has, hence, been machined in a variety of ways such as being provided with grooves or stepped portions.
In most cases, so far, the surfaces of the substrates have been mechanically machined. Therefore, the substrates must satisfy the requirements of excellent wear resistance, specular machining property, chipping resistance during the slicing and machinability.
As a material for satisfying such requirements, there has been much used an Al.sub.2 O.sub.3 -TiC sintered products obtained by adding TiC to Al.sub.2 O.sub.3. In order to satisfy the above-mentioned properties, sintering assistants such as MgO and Y.sub.2 O.sub.3 are further added to the Al.sub.2 O.sub.3 sintered product to obtain a perfectly densely sintered product which exhibits improved specular machinability, or crystalline grains of the sintered product are grown to about 1.5 to about 3 .mu.m to improve chipping resistance during the slicing and to improve machinability.
In recent years, the floating amount of the magnetic head on the magnetic recording medium is further decreasing accompanying an increase in the density of magnetic recording. This has caused the air bearing surface of the slider to be machined requiring high dimensional precision, such as surface flatness, surface coarseness, crown, camber, blending, etc. A representative example may be a TPC (transverse pressurization contour) slider and and MR slider. The conventional machining technology, however, is not capable of satisfying these requirements to a sufficient degree and, hence, a so-called ion milling method or an RIE method has been studied to execute the machining while irradiating the specular surface to be machined with ions of Ar, CF.sub.4, CCl.sub.4, BCl.sub.3, etc.
With the conventional Al.sub.2 O.sub.3 -TiC sintered product, however, the crystalline particle diameter is relatively large, i.e., from about 1.5 to about 3 .mu.m in an average particle diameter, and, hence, the sintered product is machined (etched or milled) at a small rate. Besides, the Al.sub.2 O.sub.3 and TiC particles are machined at different rate, and the surfaces after machined become far from of satisfactory quality.
From the standpoint of obtaining a perfectly dense product, furthermore, the conventional sintered product contains sintering assistants in amounts of several percent. Accordingly, sintering assistants, compound phase of sintering assistants and Al.sub.2 O.sub.3, and glass phase much exist on the grain boundaries of Al.sub.2 O.sub.3 and TiC in the sintered product. When the ion milling or the RIE machining is carried out, therefore, the grain boundary phase is preferentially etched since the compound phase and the glass phase existing in the grain boundaries are etched at very larger rates than TiC and Al.sub.2 O.sub.3. When the compound phase and the glass phase are poorly dispersed, furthermore, large dents are formed, causing the surface quality to be deteriorated after the machining.
The present inventors have forwarded the study in view of the above-mentioned problems, have discovered the fact that the sintered product can be machined at an increased rate when it is subjected to the ion milling or to the RIE machining, and the surface quality after the machining can be greatly improved compared with the conventional sintered products when the crystalline particle diameters of Al.sub.2 O.sub.3 and TiC in the sintered product are so controlled that the particle diameter of Al.sub.2 O.sub.3 is relatively larger than that of TiC, and when the particle diameters as a whole are selected to be small, and have arrived at the present invention.